Certain types of internal combustion engines, including engines that include reciprocating pistons, are typically operated by controlling either the air or fuel provided into engine cylinders. For example, spark ignition engines such as gas or gasoline engines control engine speed by metering an amount of air that is provided to the engine, measuring the amount of air, and providing a controlled amount of fuel to achieve a desired air/fuel ratio. Similarly, compression combustion engines such as diesel or oil engines control engine speed by metering the amount of fuel that is provided to the engine's cylinders. In any event, internal combustion engines require at least air and fuel to form a combustible air/fuel mixture in the engine's cylinders to operate. If providing fuel, or air, is discontinued, then engine operation would be discontinued or prevented from initiating.
In certain conditions, for example, in the presence of a failure, it is desirable to inhibit engine operation for reasons of safety. In yet other conditions, a failure in an engine component may result in an uncontrolled flow of fuel (or air) into the engine, which can create a condition of uncontrolled engine operation. One previously proposed solution at disabling engine operation during either a safety lockout or in the presence of an engine component failure is to introduce an air shutoff valve at a point in the engine's air intake system, which operates to shut off an airflow into the engine.
One example of an air shutoff valve that has been proposed in the past can be found in U.S. Pat. No. 4,546,954, which was granted on Oct. 15, 1985. This reference describes an air shutoff valve having a paddle-shaped valve element that includes a circular gate and an actuation arm. The actuation arm pivots at one end under a force of an actuator (see, e.g., FIG. 3a) to swing the gate valve into and out from an air passage opening.
One disadvantage of existing air shutoff valves such as the valve described in the '954 patent mentioned above, is that a large actuator force is required to move the valve element when the valve is required to be used. Moreover, placement of the valve on the engine's intake system, which is usually high on the engine, subjects the valve to vibration and wear of internal components such as linkages and the like.